From German patent document-open application DE-No. 0520 35 482 and German patent document - open application DE-OS No. 25 24 224, it is already known to form a caliber or rolling passage utilizing at least three grooved rolls in a star array so that the grooves of the rolls implied define a generally closed passage or caliber through which the workpiece passes during the rolling operation which is effective with a rolling force sufficient to deform the workpiece to the requisite extent.
In these patent publications, frustoconical flanks of the rolls can roll off one another so that a stable relationship between the set of rolls can be formed to increase the rolling throughput and/or increase the average reduction which can be effected in the particular set of rolls or mill stand.
A disadvantage has been noticed with such systems. From time to time the caliber or passage may be incompletely filled, e.g. as a result of the irregularity of the oncoming workpiece or some characteristic of the flow of the metal thereof, so that the workpiece is incompletely shaped.
Occasionally, the volume of the material which is forced to pass through the passage is greater than that which can be accommodated, i.e. the caliber or passage is overfilled, and the rolled profile or shape is found to have ribs extending axially along the periphery where there was incomplete junction of the grooved surfaces of the rolls. In all of these cases, the rolling force is maintained.
The rolling force is a force which can be determined, e.g. through experiment, and can be ascertained for bar stock of different dimensions, reductions of different degrees, various compositions of materials and different temperatures of the workpieces rolled. Generally the rolling force is that required, as indicated previously, to bring about the desired reduction in the workpiece or billet or semirolled product which is to be given the desired final dimensions and efforts are made not to exceed this rolling force because any increase above the rolling force is presumed to increase the wear of the apparatus.